1. Field of the Invention
The present invention relates to a seat reclining apparatus for adjustment of the seatback angle of a reclining seat.
2. Description of Related Art
Japanese Unexamined Patent Publication No. 2012-51466 discloses a known seat reclining apparatus which includes a base plate which is fixed to a seat cushion side frame, a ratchet plate (ratchet) which is fixed to a seatback side frame and provided on the inner periphery thereof with an annular internal gear, a rotational center shaft for the base plate and the ratchet plate, a plurality (three) of lock members (pawls) which are supported to be movable relative to the base plate in radial directions of the rotational center shaft, a first cam (rotational cam) which rotates with the rotational center shaft, a plurality (three) of columnar second cams (circular cams) which are installed to be movable between the lock members and the first cam, respectively, and a lock spring (spiral spring) which biases the first cam to rotate the first cam.
A plurality (three) of guide grooves are recessed on a surface of the base plate which faces the ratchet plate to extend linearly toward the outer periphery of the base plate from the center side thereof. Each of the three guide grooves is provided on both sides (both side walls) therein with a pair of flat guide surfaces, respectively, which are parallel to each other.
An outer toothed portion is formed on an outer peripheral surface of each lock member. Each lock member is installed in the associated guide groove and guided thereby so as to be movable relative to the base plate (the associated guide groove) between an engaged position in which the outer toothed portion is engaged with the internal gear of the ratchet plate and a disengaged position in which the outer toothed portion is disengaged radially inwards from the internal gear of the ratchet plate.
The first cam is rotatable between a locked position to position each lock member in the engaged position and an unlocked position to position each lock member in the disengaged position. The lock spring biases the first cam toward the locked position.
When an operating lever (hand-operated lever) which is linked with the rotational center shaft is not manually rotated, the first cam rotates toward the locked position by the rotational biasing force of the lock spring, which causes each lock member to move toward the engaged position. In addition, the rotation of the first cam toward the locked position causes the first cam to press each second cam, and subsequently, each second cam pressed by the first cam comes into contact with and presses the associated lock member toward the engaged position. This causes the outer toothed portion of each lock member to be engaged with the internal gear of the ratchet plate, and consequently, the seatback side frame (seatback) becomes non-rotatable (temporarily fixed) relative to the seat cushion side frame (seat cushion).
On the other hand, the operating lever is manually rotated against the rotational biasing force of the lock spring, the first cam moves to the unlocked position. Thereupon, the pressing force exerted on the three lock members from the three second cams is canceled, and each lock member having moved to the engaged position moves toward the disengaged position, which causes the outer toothed portion of each lock member to be disengaged from the internal gear of the ratchet plate. As a result, the seatback side frame (seatback) becomes rotatable relative to the seat cushion side frame (seat cushion).
Each second cam of the seat reclining apparatus disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 2012-51466 is contactable not only with the first cam and each lock member but also with one of the pair of flat guide surfaces of the associated guide groove.
However, the portion of each second cam which comes in contact with one of the pair of guide surfaces of the associated guide groove is a curved surface (circular arc surface), thus coming in line contact with this one guide surface, so that concentrated loads easily occur at the contact portion therebetween.
Therefore, when the seat reclining apparatus is in a locked state, if a vehicle which incorporates the seat reclining apparatus collides with another vehicle or object and this collision causes the seatback to rotate forward or rearward vigorously, there is a possibility of large concentrated loads occurring at the aforementioned line-contact portion.
To overcome this drawback, for instance, the shape of the second cam(s) can be formed into the shape that is shown in a comparative example (not known in the art) of the seat reclining apparatus shown in FIG. 27.
The second cam in this comparative example (only one second cam is shown in FIG. 27) includes a slide-contact flat surface which comes in surface contact with one of the pair of guide surfaces of the associated guide groove and a flat pressing portion which can come into surface contact with a flat pressed portion formed on the associated lock member.
In this comparative example, since each second cam includes the slide-contact flat surface (which comes in surface contact with the one guide surface of the associated guide groove), the possibility of concentrated loads occurring between each second cam and the associated guide surface is small.
However, since each second cam in the example shown in FIG. 27 includes, in addition to the slide-contact flat surface, the flat pressing portion, which can come into surface contact with the pressed portion of the associated lock member, if an error occurs between the shape of each second cam and the design shape thereof, each second cam may become positionally unstable when the first cam rotates, so that the operation of each second cam may become unsmooth.